1. Field of the Invention
This invention relates to an impeller type descent slowing device including a closed housing, a gear train, an impeller and rotation control oil or similar viscous fluid housed in the closed housing, and an input driving shaft fitted with a driving pulley about which is trained a rope or line so that upon application of a load on the line, the impeller is rotated by means of the input driving shaft in the gear train in a manner such that rotation of the impeller is restrained by the rotation control oil or similar viscous fluid to obtain a constant descent speed for the load.
2. Description of the Prior Art
Various kinds of impeller type descent slowing devices, each having a housing accommodating a gear train and an impeller immersed in rotation control oil so as to restrain rotation of the impeller by viscous action of the oil to cause a load to lower slowly, have been suggested in Japanese Examined Patent Publication (Kokoku) Nos. 52-20,483 and 56-37,836 and a Japanese Unexamined Patent Publication (Kokai) No. 55-103,871. Publication Nos. 52-20,483 and 56-37,836 disclose rotation control oils themselves and describe that such oils are used for reduction devices in which the oils are stirred by a number of gears. Details of the impeller are not necessarily made clear in these publications, however.
Japanese Unexamined Patent Publication No. 55-103,871 discloses a mechanism somewhat similar to that of the present invention, which comprises an input driving shaft, an impeller, rotation control oil, and pendulum pulleys; but this unexamined Publication does not clarify the following aspects: (1) the optimum rotating ratio between the impeller and the input driving shaft; (2) volumetric capacities of a housing and gears, with an impeller and metal support assumed to be contained in the housing; (3) the shape and area of blades; and (4) the use of an auxiliary mechanism for ensuring slow descent irrespective of existing temperature and load differentials.
Regarding aspect (1), the rotating ratio is governed by the necessary descent speed of a load (for example, a person), the mechanism working through means of a line extending around a driving pulley fitted on an input driving shaft; with rotation control oil in a housing, rotating force transmitted from the input driving shaft is transmitted to the impeller that in turn rotates. Highly viscous rotation control oil provides resistance to rotation to ensure a safe descent speed. In other cases, such as the descent of dry goods or the like, it is not necessary that the rotation be particularly slow. In order to obtain a slow descent speed within a certain range and to avoid excess acceleration and deceleration, an optimum rotating ratio is therefore required.
Regarding aspect (2), the optimum capacities of the housing and components therein must be determined in order to apply it to practical use and to prevent extraordinary temperature rise of the rotation control oil.
Regarding aspect (3), two, three, and four blade impellers are considered useful configurations. It is important to determine the most preferable shape of the impeller and the optimum blade area associated with kinds of rotation control oil.
Regarding aspect (4), the temperature and load are important factors in practical use. Rotation control oil whose viscosity does not vary with changes in temperature is ideal for this use, but such an oil does not exist. An auxiliary mechanism therefore is necessary to prevent increases and decreases in descent speed due to viscosity changes governed by temperatures changes and for preventing speed changes linked to load changes. Japanese Unexamined Patent Publication No. 55-103,871 does not consider these factors, and therefore its structure results in great difficulties during practical use.